The entrance is meh, you've got to go deeper to get beyond the crowds. Be prepared for traffic coming into the forest. Especially on weekends.
I only explored the entrance of the forest, which seemed to be overflowing with picnickers barbecuing their kebabs. I will go back and try to go deeper into the forest where there is less meat grilling. Also, I'll visit the dam and little lake / big pond a few kilometers in.
If you bring a car and are not daunted by the traffic (which isn't so bad, I just don't like traffic) take the road to the left when it splits at the entrance of the park. Another option is to visit the Ataturk Aboretum. The is a small fee to enter, but no meat grilling and smoke read more